Interpretive Summary: Some crop species accumulate higher levels of cadmium in their edible portions than desired for use as food, and excessive diet Cd has caused adverse health effects for subsistence rice consumers. Because of concern about potential excessive dietary cadmium, limits have been established by some nations on maximum allowed levels of cadmium in some grains. Certain production districts include soils which because of natural soil cadmium enrichment, or soil properties, cause grains to exceed these set limits. Durum wheat, flax, nonoilseed sunflower, and rice are the crops most commonly exceeding cadmium limits. One approach to help growers produce crops with acceptable cadmium levels is to breed crop genotypes with lower cadmium concentration. This paper summarizes information on genetic variation in crop cadmium accumulation, and methods to breed lower cadmium genotypes of crops for which evidence has been obtained. Further, the review considers the cost of producing lower cadmium crop cultivars, and methods needed to continue the production of lower cadmium crops. Considerable success has been made with development of new cultivars with lower cadmium for durum wheat and nonoilseed sunflower. Evidence has been obtained that lower cadmium cultivars of rice, soybean, lettuce and some other crops could be bred using information and techniques already developed, but that such improved cultivars ready for growers to use have not yet become available.

Technical Abstract:
Natural variation occurs in the uptake and distribution of essential and nonessential trace elements among crop species and among cultivars within species. Such variation can be responsible for trace element deficiencies and toxicities, which in turn can affect the quality of food. Plant breeding can be an important tool to both increase the concentration of desirable trace elements and reduce that of potentially harmful trace elements such as cadmium (Cd). Selection programs for a low Cd content of various crops, including durum wheat, sunflower, rice and soybean have been established and low-Cd durum wheat cultivars and sunflower hybrids have been developed. In durum wheat (Triticum turgidum L. var durum), low Cd concentration is controlled by a single dominant gene. The trait is highly heritable, and incorporation of the low-Cd allele can help to reduce the average grain Cd to levels below proposed international limits. The allele for low Cd concentration does not appear to affect major economic traits and should not cause problems when incorporated into durum cultivars. The cost of Cd selection in a breeding program is initially large both in terms of Cd determination and reduced progress towards development of other economic traits, but declines as more breeding lines in the program carry the low-Cd trait and are utilized in new crosses. Production of low-Cd crop cultivars can be used as a tool to reduce the risk of movement of Cd into the human diet.